Toyota Repair: repetitive buzzing noise from ABS module when engine off, side fender, automatic tranny

Question
Greetings Ted - two months ago I bought a very nice 1996 4Runner Limited edition 3.4 V6 4-wheel drive automatic tranny with 145k miles. Exceptionally clean unit from a reputable dealer. After about a week of driving I realized there always occurs a small repetitive buzzing sound that starts about  2-3 minutes after shutting off the engine. The low buzz is for about 2 seconds, then repeats about every 50 seconds for about an hour then gradually the time intervals between buzzing grow longer. I have heard it still buzzing 23 hours after turning off the engine. Listening with a mechanics stethoscope I determine it is coming from the interior of the ABS module mounted on the driver's side fender well of the engine bay. It sounds like a pressure bleed-off but may be an electrical discharge.  The truck runs well, brakes are very effective, and no lights display or trouble codes found.  Is this something normal or something serious?  It's now getting annoying because I don't know what it is or if I should be worried about it.  I appreciate your helpfulness and experience and look forward to an answer.  Thanks!

Answer
Hello, although some noise after shutting the engine off may be normal but not more than a few seconds, since no warning lights are on the problem seems to be internal to the abs actuator and seems hydraulic fluid related, I have not experience a problem exactly like this so I can only make a suggestion and best guess, I think the abs actuator will most likely have to be replaced to resolve this, since the brakes are working fine and there are no warning lights it doesn't seem to be a safety concern, this is a very expensive part so I would assume that it was traded in because the previous owner did not put that kind of money into it (parts and labor about $2000)Have you approached the selling dealer with this? Did you buy a warranty contract? I would contact the dealer and ask them to check into this but I think they will most likely come up with the same answer.